Gutters alone won’t solve problems in cold weather climates — gutter apron, sometimes called gutter flashing, is also important to prevent rot of your fascia.
Fascia is that piece of wood, just behind the gutter. In most homes, the gutter is flush with the fascia.
Gutter apron is a piece “L” shaped material, usually aluminum, that goes up under the shingle and hangs down along the fascia. This allows rain water to drip off of the shingles and onto the gutter apron, then directly into the gutter.
Gutter apron is also needed for rubber roofs, but in that case, the rubber from the roof can simply be set to hang down into the gutter. The gutter comes up under the edge of the rubber and then an aluminum bar called a termination bar, sometimes referred to as a t-bar, is fastened through the rubber and the back of the gutter and into the fascia. Optimally this is tight as the fascia underneath the rubber should be flat. The screws with the t-bar compresses the rubber down against the fascia, essentially sandwiching the layers. That is to say that you have t-bars, then rubber, then the gutter, then the fascia all being pressed together in order to keep out water.
Of course there are exceptions to the rule. Hanging style gutters have to be applied to homes that don’t have traditional vertical fascia. This type is most common in homes built prior to about 1940. Victorian style homes almost all have this angled fascia and because applying a gutter to an angled fascia would just let the water flow right over the edge of the home, hanging style, which allows the top of the gutter to remain mostly parallel to the ground, catches the rainfall.